1. Field of the Invention
This invention relates to mechanical printers, and more specifically to character printing mechanisms of the dot matrix type. 2. History of the Prior Art
Mechanical printing systems, particularly those known as line printers, have been widely used in the data processing industry. Many such systems are of the moving character type employing formed character images on a member which is moved relative to the paper so as to present a desired type position for an impacting action between the character image and paper. Other systems have been of the wire matrix type in which a printer head is used that has a number of separately actuable print wires, one for each possible vertical position within a matrix.
Dot matrix printers employing a movable hammer bank, as evidenced for example by U.S. Pat. No. 3,782,278, have proven to have a number of advantages over other systems. Particularly advantageous is a system of this type disclosed in a co-pending application, Ser. No. 495,830, Barrus et al, Printer System, filed Aug. 8, 1974 and assigned to the assignee of the present application. In the printer system disclosed in Ser. No. 495,830 each of a plurality of hammers scans a number of dot printing positions within a dot matrix line and is energized at a high repetition rate during movement to imprint serially the dot patterns in that line for several successive characters. The paper is then advanced and the next dot matrix line is printed in the reverse direction. The hammers are mounted within a shuttle mechanism which is driven in a trapezoidal velocity profile from a cam system that also engages an oppositely moving counterweight system. The hammer bank is comprised of plural hammer elements and associated magnetic actuators. The hammer elements which are normally magnetically biased to a retract position by a permanent magnet are selectively released for imprinting by the magnetic actuators which neutralize the magnetic field from the permanent magnet.
The present invention provides certain alternatives and improvements to a hammer bank or mechanism of the type shown in application Ser. No. 495,830.